Brake system for electrically operated vehicles

ABSTRACT

A braking and driving system for electrically operated vehicles including an electric motor for driving the vehicle which may be operated as a generator to provide additional braking and recovery of braking energy by charging the battery. Hydraulic braking on the drive axle is delayed until the maximum level of electromotive braking is reached. This allows the design distribution of braking between the front and rear axles to be maintained while insuring a maximum recovery of braking energy through charging of the battery.

United States Patent inventors Heinrich Oberthur Offenbach-Rumpenheim;Otto Depenheuer, Bad Homburg, both of Germany Appl. No. 860,605

Filed Sept. 24, 1969 Patented Nov. 23, 1971 Assignee InternationalTelephone and Telegraph Corporation New York, NY.

Priority Sept. 28, 1968 Germany P 17 88 077.2

BRAKE SYSTEM FOR ELECTRICALLY OPERATED VEHICLES 5 Claims, 6 DrawingFigs.

11.8. CI 180/65 R, 188/156, 192/2, 303/3, 318/139, 318/371 Int. Cl86017/24 Field of Search 180/65;

FRONT WHEEL 9 BRAKE CYLINDER BATTERY SPEED CONTROL PEDAL [56] ReferencesCited UNITED STATES PATENTS 2,118,412 5/1938 McCune 188/159 UX 2,348,0535/1944 Bowker 180/65 X 3,114,871 12/1963 Schenk1eberger.. 180/65 X3,171,505 3/1965 lmelmann 180/65 FOREIGN PATENTS 391,890 5/1933 GreatBritain 303/3 Primary Emminer-Benjamin Hersh Assistant Examiner-MiltonL. Smith Attorneys-C. Cornell Remsen, Jr., Walter J. Baum and Paul W.Hemminger ABSTRACT: A braking and driving system for electricallyoperated vehicles including an electric motor for driving the vehiclewhich may be operated as a generator to provide additional braking andrecovery of braking energy by charging the battery. Hydraulic braking onthe drive axle is delayed until the maximum level of electromotivebraking is reached. This allows the design distribution of brakingbetween the front and rear axles to be maintained while insuring amaximum recovery of braking energy through charging of the battery.

REAR WHEEL BRAKE CYLINDEIR ABSORBING PISTON 8 9 FRONT WHEEL BRAKECYLINDER REAR WHEL 0 BRAKE CYLINDER BRAKE SYSTEM FOR ELECTRICALLYOPERATED VEHICLES BACKGROUND OF THE INVENTION The invention relates tobraking systems for electrically operated vehicles and particularly tosystems which utilize an electric motor acting as a generator to provideadditional braking and to recover braking energy by charging thebattery.

Conventional small electrically operated vehicles in general possessthree separate braking systems: a hydraulic service brake, a mechanicalparking brake, and, in addition, an electromotive brake if the motorfunctions as a generator, in which case part of the energy issimultaneously recovered and fed into the battery. In these systems theelectromotive brake effects only a fraction of the total requiredbraking.

Also known is an eddy current brake in which the resistance to rotationis produced by eddy currents generated by the rotation of metal disks ina magnetic field of force. In contrast with the electromotive brake norecovery of energy is possible with eddy current brakes.

SUMMARY OF THE INVENTION It is an object of this invention to provide abraking system for an electrically operated vehicle in which theelectric motor for driving the vehicle may act as a generator to providesupplemental braking without affecting the designed distribution ofbrake force between the front and rear vehicle axles and in which thebraking energy produced by the electric motor acting as a generator isrecovered by charging the battery.

, It is a further object of this invention to provide an electricallyoperated vehicle in which an electric motor acting as a generatorprovides braking for at least one axle prior to the application of thehydraulic brakes to the wheels of that axle.

It is a further object of this invention to provide a system of thistype in which the hydraulic brakes do not become effective until themaximum braking force obtainable through the electric motor acting as agenerator has been attained, thereby maximizing the braking energy whichmay be recovered by charging the battery.

These objects are achieved in an electrically operated vehicle having anelectric motor drive by providing an electric motor which may act as agenerator and which is connected to the battery through an electriccontrol which is responsive to the position of a speed control pedal formotor operation and which is connected to the hydraulic brake system ofthe vehicle by means of a second electric control device which isresponsive to the hydraulic brake pressure so as to interrupt theoperation as an electric motor and control its operation as a generatorto provide braking and charging of the battery.

To insure that the maximum braking energy which may be recovered throughthe charging of the battery is actually recovered, the application ofthe hydraulic brakes may be delayed with respect to the braking effectof the electric motor acting as a generator. If the vehicle hasrear-wheel drive, the

- electric motor has a hydraulic torque-absorbing support acting toprevent rotation of the electric motor when braking takes place. Thepressure developed in the hydraulic support acts on a balancing valve inthe hydraulic brake system to prevent the application of the rear wheelbrakes until the torque in the electric motor operating as a generatorhas reached its maximum value.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a diagrammaticrepresentation of a braking system for an electrically operated vehiclewith rear wheel drive.

FIG. 2 is a diagrammatic representation of the hydraulic supports forthe electric motor.

FIG. 3 is a diagrammatic representation of a braking system for anelectrically operated vehicle with all-wheel drive.

FIG. 4 depicts the distribution of braking force to the front and backaxle. The possible characteristic curve of electromotivc braking isdrawn in on the back axle but not considered as part of the totalbraking.

FIG. 5 is a diagrammatic representation of the desired brake forcedistribution with regard to the electromotive braking on the back axleof an electrically operated vehicle with rearwheel drive.

FIG. 6 is a diagrammatic representation of the desired brake forcedistribution of an electrically operated vehicle with allwheel drive.

DESCRIPTION OF THE PREFERRED EMBODIMENTS It is well known that anelectric motor can be designed so that it may be driven as a generatorwhen separated from its power supply to produce electric energy andprovide a braking efiect.

FIG. 4 shows the relationship between the braking effects on the frontand rear axles of a vehicle and the possible braking on the rear axlewheels by means of an electric motor operating as a generator. Althoughthe braking effect of the electric motor operating as a generator is notshown as part of the total braking on the front and rear axles, it willbe apparent that the curve of total braking would show an abrupt changein slope if the electric motor braking effect, which increases withbrake pressure until it levels off at some maximum value, were merelyadded to the normal hydraulic braking on the rear axle wheels.

According to this invention, as shown in FIG. 5, the operation of thehydraulic brakes on the rear wheel is delayed until the maximum brakingeffect of the electric motor acting as a generator is obtained so as tomaintain the designed distribu tion of brake force between the front andrear axles and to insure maximum recovery of braking energy.

Thus, in the case of an electrically operated vehicle with rear-wheeldrive, hydraulic brake pressure is applied to the brake cylinders of thefront axle immediately upon commencement of braking while rear axlewheels are braked by means of the electric motor acting as a generator.Only after the braking effect of the electric motor has reached itsmaximum value do the hydraulic brakes on the rear wheels becomeactivated. Hydraulic braking on the rear wheels then adds to theelectric motor braking, which remains constant as brake pressureincreases. In order to obtain the intended brake force distributionbetween the axle, the hydraulic braking on the rear wheels must increasewith increased brake pressure at the same rate as the electric motorbraking increased to its maximum value.

FIG. 1 show the invention embodied in a braking system for anelectrically operated vehicle having a rear-wheel drive.

The electric motor and hydraulic brakes are integrated into a commonsystem. The electric motor 2 which drives the rear axles is connected toa battery I via a service brake interrupter 5 and an electric control 3,which is responsive to the mechanical operation of a speed control pedal11. The position of the speed control pedal determines the driving speedof the series wound electric motor.

The hydraulic braking system comprises a tandem master A cylinder 6which is actuated by a brake pedal 12. The tandem master cylinder isconnected to the wheel brake cylinders 9 of the front axle wheelsdirectly and with the wheel brake cylinders 10 of the rear axle througha valve 7 which is opened to allow braking on the rear wheels only whenthe pressure in hydraulic line 15 exceeds a predetennined value. Thehydraulic line 15 is connected to hydraulic piston torque-absorbingsupports 8 of the electric motor so that the pressure in the hydraulicline 15 is a function of the torque generated by the electric motoracting as a generator. This is shown in FIG. 2. When the electric motoris operated as a motor, it is supported by the firm bearings 16. Howeverwhen the electric motor functions as a generator, the torque generatedby the electric motor is reversed and the electric motor is supported bythe hydraulic supports 8 which produce a hydraulic pressure which is afunction of the braking torque produced.

The service brake interrupter 5 and a second electric control 4 areconnected to the hydraulic brake system via line 18 and a two-way valve13 which receives a pressure signal from both the hydraulic line leadingto the front wheels and from the hydraulic line leading to the rearwheels.

The system shown in FIG. 1 operates as follows. When the speed controlpedal is depressed by the operator, the electric motor 2 is connected tothe battery via the electric control 3 which is mechanically connectedto the speed control pedal. When the brake pedal 12 is actuated,hydraulic brake pressure developed in the tandem master cylinder 6 istransmitted to the front wheel brakes. However, the pressure in the rearwheel brake circuit is transmitted only as far as the valve 7, which isinitially closed. The hydraulic brake pressure is also transmitted tothe electric control device 4 and the service brake interrupter 5. Theservice brake interrupter disconnects the electric motor from thebattery as a source of power while the electric control 4 regulates thefunction of the electric motor as a generator. The two-way valve 13 isconnected so that it may be actuated by the hydraulic pressure in eitherthe front wheel or rear wheel circuits and will isolate either circuitif it becomes inoperative while still actuating the service brakeinterrupter 5 and the electric control 4.

The electric control 4 includes a transducer which controls the electricmotor operating as a generator as a function of the brake pressureexerted by the brake pedal 12. The electric motor is driven by thekinetic energy of the vehicle and acts as a brake via an inductive linkwhich has a characteristic curve which gives the desired distributionbetween front and rear axle braking. The electric control 4 is connectedto the battery to enable the electricity produced by the electric motoracting as a generator to be recovered by charging the battery 1.

Due to the hydraulic supports 8 for the electric motor described above,the torque produced by the electric motor when operating as a generatorwill increase the pressure in line until the maximum electromotivebraking is reached. At this point the balancing valve 7 is set to opento allow the pressure generated in the master cylinder to be transmittedto the rear axle brakes. Thus, hydraulic braking is provided on the rearwheels in addition to the braking of the electric motor acting as agenerator.

FIG. 3 shows the invention embodied in a vehicle with allwheel drive.Except as described below, this system is identical to that shown inFIG. 1.

The braking forces produced by the electric motor acting as a generatorare evenly distributed to the front and rear axle brakes. The brakingeffect of the hydraulic brakes is retarded so that the hydraulic brakesare not applied until the braking effect of the electric motor acting asa generator has reached it maximum value. This may be accomplished byproviding an electric control 4 which responds immediately to hydraulicbrake pressure and a throttling of the hydraulic brakes to delay theirreaction to brake pressure. The throttling devices are shownschematically by the elements 19 and 20 in the front and rear brakecircuits respectively. The operation of the system of FIG. 3 is showngraphically in FIG. 6.

Although the above embodiments show a single electric motor for thevehicle, it will be obvious that several electric motors may be providedfor individual wheels or separate axles with a similar braking systemoperating as described above.

It will be appreciated that the invention illustrated and describedherein may be modified by those skilled in the art without deviatingfrom the spirit and scope of the invention as set forth in the followingclaims.

We claim as our invention:

1. A driving and braking system for electrically operated wheeledvehicles comprising:

a hydraulic braking system for the vehicle including a master cylinder,hydraulic brake circuits coupled to said master cylinder and a brakepedal actuated by the operator to produce hydraulic brake pressure insaid master cylinder;

a battery;

an electric motor connected between the battery and vehicle-drivingaxle; and

electric control means responsive to the position of a speed controlpedal for controlling the flow of current from the battery to theelectric motor to drive the vehicle and responsive to said hydraulicbrake pressure in said master cylinder upon operation of said brakepedal for interrupting the current to the electric motor and forcontrolling the flow of current from the electric motor operating as agenerator to the battery to provide additional braking whilesimultaneously charging the battery.

2. A driving and braking system for electrically operated wheeledvehicles comprising:

a hydraulic braking system for the vehicle;

a battery;

an electric motor connected between the battery and vehicle-drivingaxle;

electric control means responsive to the position of a speed controlpedal for controlling the flow of current from the battery to theelectric motor to drive the vehicle and responsive to the brake pressurein the hydraulic brake system for interrupting the current to theelectric motor and for controlling the flow of current from the electricmotor operating as a generator to the battery to provide additionalbraking while simultaneously charging the battery; and

means responsive to the mechanical torque produced by the electric motoroperating as a generator for preventing the brake pressure in thehydraulic brake system from being applied to the brakes until saidtorque exceeds a predetermined value.

3. The driving and braking system of claim 2, wherein the vehicle hasrear-wheel drive and the means responsive to said torque produced by theelectric motor acting as a generator prevents said brake pressure frombeing applied to the rear wheels while permitting the immediateapplication of the front wheel brakes.

4. A driving and braking system for electrically operated wheeledvehicles comprising:

a hydraulic braking system for the vehicle;

a battery;

an electric motor connected between the battery and vehicle-drivingaxle;

electric control means responsive to the position of a speed controlpedal for controlling the flow of current from the battery to theelectric motor to drive the vehicle and responsive to the brake pressurein the hydraulic brake system for interrupting the current to theelectric motor and for controlling the flow of current from the electricmotor operating as a generator to the battery to provide additionalbraking while simultaneously charging the battery; and

means responsive to the torque produced by the electric motor operatingas a generator for preventing the brake pressure in the hydraulic brakesystem from being applied to the brakes until the torque exceeds apredetermined value; said means responsive to the torque includingelectric motor supports which generate a pressure signal which is afunction of the torque when the electric motor operates as a generatorand a valve in the hydraulic brake system responsive to the pressuresignal for preventing the brake pressure in the hydraulic brake systemfrom being applied to the brakes until the pressure signal exceeds apredetermined value.

5. A driving and braking system for electrically operated wheeledvehicles comprising:

a hydraulic braking system for the vehicle;

a battery;

an electric motor connected between the battery and vehicle-drivingaxle;

electric control means responsive to the position of a speed controlpedal for controlling the flow of current from the battery to theelectric motor to drive the vehicle and responsive to the brake pressurein the hydraulic brake system for interrupting the current to theelectric motor applied to the rear wheels while permitting the immediateapplication of the front wheel brakes;

said means responsive to the torque including electric motor supportswhich generate a pressure signal which is a function of the torqueproduced when the electric motor operates as a generator and a valve inthe hydraulic brake line to the rear wheels responsive to the pressuresignal for preventing the brake pressure in the hydraulic brake systemfrom being applied to the rear wheel brake until the pressure signalexceeds a predetermined value.

1. A driving and braking system for electrically operated wheeledvehicles comprising: a hydraulic braking system for the vehicleincluding a master cylinder, hydraulic brake circuits coupled to saidmaster cylinder and a brake pedal actuated by the operator to producehydraulic brake pressure in said master cylinder; a battery; an electricmotor connected between the battery and vehicledriving axle; andelectric control means responsive to the position of a speed controlpedal for controlling the flow of current from the battery to theelectric motor to drive the vehicle and responsive to said hydraulicbrake pressure in said master cylinder upon operation of said brakepedal for interrupting the current to the electric motor and forcontrolling the flow of current from the electric motor operating as agenerator to the battery to provide additional braking whilesimultaneously charging the battery.
 2. A driving and braking system forelectrically operated wheeled vehicles comprising: a hydraulic brakingsystem for the vehicle; a battery; an electric motor connected betweenthe battery and vehicle-driving axle; electric control means responsiveto the position of a speed control pedal for controlling the flow ofcurrent from the battery to the electric motor to drive the vehicle andresponsive to the brake pressure in the hydraulic brake system forinterrupting the current to the electric motor and for controlling theflow of current from the electric motor operating as a generator to thebattery to provide additional braking while simultaneously charging thebattery; and means responsive to the mechanical torque produced by theelectric motor operating as a generator for preventing the brakepressure in the hydraulic brake system from being applied to the brakesuntil said torque exceeds a predetermined value.
 3. The driving andbraking system of claim 2, wherein the vehicle has rear-wheel drive andthe means responsive to said torque produced by the electric motoracting as a generator prevents said brake pressure from being applied tothe rear wheels while permitting the immediate application of the frontwheel brakes.
 4. A driving and braking system for electrically operatedwheeled vehicles comprising: a hydraulic braking system for the vehicle;a battery; an electric motor connected between the battery andvehicle-driving axle; electric control means responsive to the positionof a speed control pedal for controlling the flow of current from thebattery to the electric motor to drive the vehicle and responsive to thebrake pressure in the hydraulic brake system for interrupting thecurrent to the electric motor and for controlling the flow of currentfrom the electric motor operating as a generator to the battery toprovide additional brakinG while simultaneously charging the battery;and means responsive to the torque produced by the electric motoroperating as a generator for preventing the brake pressure in thehydraulic brake system from being applied to the brakes until the torqueexceeds a predetermined value; said means responsive to the torqueincluding electric motor supports which generate a pressure signal whichis a function of the torque when the electric motor operates as agenerator and a valve in the hydraulic brake system responsive to thepressure signal for preventing the brake pressure in the hydraulic brakesystem from being applied to the brakes until the pressure signalexceeds a predetermined value.
 5. A driving and braking system forelectrically operated wheeled vehicles comprising: a hydraulic brakingsystem for the vehicle; a battery; an electric motor connected betweenthe battery and vehicle-driving axle; electric control means responsiveto the position of a speed control pedal for controlling the flow ofcurrent from the battery to the electric motor to drive the vehicle andresponsive to the brake pressure in the hydraulic brake system forinterrupting the current to the electric motor and for controlling theflow of current from the electric motor operating as a generator to thebattery to provide additional braking while simultaneously charging thebattery; means responsive to the torque produced by the electric motoroperating as a generator for preventing the brake pressure in thehydraulic brake system from being applied to the brakes until the torqueexceeds a predetermined value; wherein the vehicle has rear-wheel driveand the means responsive to torque produced by the electric motor actingas a generator prevents the brake pressure from being applied to therear wheels while permitting the immediate application of the frontwheel brakes; said means responsive to the torque including electricmotor supports which generate a pressure signal which is a function ofthe torque produced when the electric motor operates as a generator anda valve in the hydraulic brake line to the rear wheels responsive to thepressure signal for preventing the brake pressure in the hydraulic brakesystem from being applied to the rear wheel brake until the pressuresignal exceeds a predetermined value.